Cervical Plexus — Formation and Branches
Formation
- Formed by the ventral (anterior) rami of C1, C2, C3, C4 spinal nerves
- Located in the neck deep to the internal jugular vein and SCM, on the surface of scalenus medius and levator scapulae
- Each nerve (except C1) divides into ascending and descending branches that unite with adjacent nerves to form loops
Branches
Superficial (Cutaneous) Branches — All emerge at Erb’s Point
Erb’s Point = Nerve Point of Neck = junction of upper 1/3 and lower 2/3 of posterior border of SCM
| Nerve | Root | Distribution |
|---|---|---|
| Lesser occipital | C2 | Scalp behind auricle; upper part of medial surface of auricle |
| Great auricular | C2, C3 | Skin over parotid gland, lower auricle, angle of jaw, mastoid area |
| Transverse cutaneous (anterior cutaneous) | C2, C3 | Anterior triangle of neck, front of neck (C-shaped distribution) |
| Supraclavicular (3 branches: medial, intermediate, lateral) | C3, C4 | Skin over clavicle, shoulder tip, upper pectoral region |
Deep (Motor) Branches
| Nerve | Root | Muscles Supplied |
|---|---|---|
| Phrenic nerve | C3, C4, C5 (mainly C4) | Diaphragm (sole motor supply) |
| Ansa cervicalis (superior root = descendens hypoglossi C1, inferior root C2,C3) | C1, C2, C3 | Sternohyoid, sternothyroid, omohyoid (infrahyoid strap muscles) |
| Muscular branches to: | ||
| — Rectus capitis lateralis | C1 | — |
| — Rectus capitis anterior | C1 | — |
| — Longus capitis | C1, C2, C3 | — |
| — Longus colli | C2, C3, C4 | — |
| — Levator scapulae (part) | C3, C4 | — |
| — Scalenus medius (part) | C3, C4 | — |
Phrenic Nerve — Details
- Roots: C3, C4, C5 (mnemonic: “C3,4,5 keep the diaphragm alive”)
- Course in neck: Descends on scalenus anterior (under prevertebral fascia), passes behind subclavian vein, enters thorax through superior thoracic aperture
- Clinical:
- Injury → ipsilateral diaphragm paralysis (elevated on X-ray)
- Referred pain from diaphragm → tip of shoulder (C4 dermatome)
- Phrenic nerve palsy from lung carcinoma, mediastinal masses
- Hiccup = phrenic nerve irritation
Ansa Cervicalis
- A nerve loop formed by:
- Superior root (descendens hypoglossi): C1 fibres running with CN XII
- Inferior root (descendens cervicalis): C2 + C3 fibres
- Lies superficial to carotid sheath
- Supplies all infrahyoid strap muscles except thyrohyoid (supplied by C1 fibres via hypoglossal nerve)